Thursday 25 July 2013 11.55 EDT
First published on Thursday 25 July 2013 11.55 EDT

US Attorney general Eric Holder announced Thursday that the Justice Department is opening a new front in the battle for voter protections, a response to the supreme court ruling that he said dealt a major setback to the Voting Rights Act.

In a speech to the National Urban League in Philadelphia, Holder said that as its first move, the department is asking a federal court in San Antonio to require the state of Texas to obtain advance approval before putting future political redistricting changes in place.

The attorney general called the Voting Rights Act "the cornerstone of modern civil rights law" and said that "we cannot allow the slow unraveling of the progress that so many, throughout history, have sacrificed so much to achieve".

The supreme court, on a 5-4 vote, threw out the most powerful part of the landmark Voting Rights Act, the law that became a major turning point in black Americans' struggle for equal rights and political power.

The move in Texas is the Justice Department's first action to further safeguard voting rights following the Supreme Court decision on June 25, said Holder, "but it will not be our last".

"Even as Congress considers updates to the Voting Rights Act in light of the court's ruling, we plan, in the meantime, to fully utilize the law's remaining sections to ensure that the voting rights of all American citizens are protected," Holder said.

The requirement to obtain advance approval from either the department or a federal court before changing voting laws is available under the Voting Rights Act when intentional discrimination against voters is found.

The section of the Voting Rights Act Holder invoked can be applied to all types of voting changes – from moving the location of a polling place to imposing stringent requirements such as photo identification at the polls.

In the Texas case, the department is not directly intervening but is filing what's known as a statement of interest in support of the private groups that have filed suit.

Holder said that based on evidence of intentional racial discrimination presented last year in a redistricting case in Texas, "we believe that the state of Texas should be required to go through a preclearance process whenever it changes its voting laws and practices".

In Texas, there is a history of "pervasive voting-related discrimination against racial minorities," Holder added.

A three-judge panel in San Antonio has been looking at Texas voting maps since 2011, when the court threw out boundaries drawn by a then-GOP supermajority in the statehouse.

Under the direction of Republican governor Rick Perry last month, the Legislature ratified those interim maps as permanent over the objection of Democrats, who still believe the maps are biased and underrepresent minorities.

Aides to Perry and Texas attorney general Greg Abbott did not immediately return messages seeking comment.